In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be abl...In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.展开更多
Fractional frequency reuse(FFR) has recently emerged as an efficient inter-cell interference coordination technique for orthogonal frequency division multiple access(OFDMA) based multi-tier cellular networks due to it...Fractional frequency reuse(FFR) has recently emerged as an efficient inter-cell interference coordination technique for orthogonal frequency division multiple access(OFDMA) based multi-tier cellular networks due to its low complexity, minimal signaling over-head, and coverage improvement. In this work, an intermediary region(IR) at the border of the center region(CR) and edge region(ER) is defined, which prevents severe cross-tier interference and is usually ignored by other schemes. Furthermore, a strategic resource allocation scheme is proposed, which allows macro users in this new region to be served more resources due to their good channel conditions close to the serving base station(BS), while femto users are assigned resource blocks from sub-bands that receive the least net interference from a set of usable sub-bands in any region. We find by analysis and simulation the optimal threshold for IR, which minimizes the cross-tier interference, and show that the femto throughput is also maximized for this threshold. Numerical results show the proposed scheme outperforms other notable schemes in terms of throughput and outage performances.展开更多
The cdma2000 1xEV-DO mobile communication system provides broadcast and multicast services(BCMCS) to meet an increasing demand for multimedia data services.Single frequency network(SFN) is recognized as an effective w...The cdma2000 1xEV-DO mobile communication system provides broadcast and multicast services(BCMCS) to meet an increasing demand for multimedia data services.Single frequency network(SFN) is recognized as an effective way to improve the spectral efficiency of the BCMCS system.To improve the coverage and the data rate of the BCMCS users,an interference cancellation algorithm based on macro diversity is introduced in this paper.The performance of BCMCS in CDMA2000 EV-DO networks under the condition of SFN is evaluated.The simulation results show a significant improvement in bit error ratio(BER) while quantitatively validating the efficiency of our approach.展开更多
文摘In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.
基金supported by the National Major Project under Grant No.2015ZX03001013-002
文摘Fractional frequency reuse(FFR) has recently emerged as an efficient inter-cell interference coordination technique for orthogonal frequency division multiple access(OFDMA) based multi-tier cellular networks due to its low complexity, minimal signaling over-head, and coverage improvement. In this work, an intermediary region(IR) at the border of the center region(CR) and edge region(ER) is defined, which prevents severe cross-tier interference and is usually ignored by other schemes. Furthermore, a strategic resource allocation scheme is proposed, which allows macro users in this new region to be served more resources due to their good channel conditions close to the serving base station(BS), while femto users are assigned resource blocks from sub-bands that receive the least net interference from a set of usable sub-bands in any region. We find by analysis and simulation the optimal threshold for IR, which minimizes the cross-tier interference, and show that the femto throughput is also maximized for this threshold. Numerical results show the proposed scheme outperforms other notable schemes in terms of throughput and outage performances.
文摘The cdma2000 1xEV-DO mobile communication system provides broadcast and multicast services(BCMCS) to meet an increasing demand for multimedia data services.Single frequency network(SFN) is recognized as an effective way to improve the spectral efficiency of the BCMCS system.To improve the coverage and the data rate of the BCMCS users,an interference cancellation algorithm based on macro diversity is introduced in this paper.The performance of BCMCS in CDMA2000 EV-DO networks under the condition of SFN is evaluated.The simulation results show a significant improvement in bit error ratio(BER) while quantitatively validating the efficiency of our approach.
